Method and equipment for limitation of the coating width and/or for prevention of damage to the roll ends in coating or surface-sizing of paper or of an equivalent web material

Abstract: The invention concerns a method for limitation of the coating width and/or for prevention of damage to the roll ends in coating or surface-sizing of paper or of an equivalent web material. In the method, the coating agent, such as size, coating paste or equivalent, is introduced into the coating device to an application zone defined by a coating member (10), by a moving base (1), by lateral seals (20), and by a front wall (15) and spread onto the moving base by means of the coating member (10) loaded against the moving base. Into the areas outside the coating width, substantially over the width defined by the lateral seals and the roll ends, liquid is sprayed onto the moving base (1), in its running direction, immediately before the coating member (10) or directly into the nip between the moving base (1) and the coating member (10). The liquid jets are supposed to lubricate said nip and to dilute the coating agent that has entered into the areas outside the coating width. The excess amount of the sprayed liquid is collected off to prevent its entering into the recirculation of the coating agent, so as to prevent the coating agent from being diluted. The invention also concerns a corresponding equipment.

Description: The invention concerns a method for limitation of the coating width and/or for prevention of damage to the roll ends in coating or surface-sizing of paper or of an equivalent web material, in which method the coating agent, such as size, coating paste or equivalent, is introduced into the coating device to an application zone defined by a coating member, by a moving base, by lateral seals, and by a front wall and spread onto the moving base, such as a roll face or a paper or board web that is passed over the roll, by means of the coating member loaded against the moving base. The invention also concerns an equipment for limitation of the coating width and/or for prevention of damage to the roll ends in coating or surface-sizing of paper or of an equivalent web material in a coating device, which comprises an application zone defined by a coating member, by a moving base, such as a roll face or a paper or board web that is passed over the roll, by lateral seals, and by a front wall, the coating member that is loaded against the moving base being fitted to spread and to smooth the coating agent, such as size, coating paste or equivalent, which has been introduced into the application zone, onto the moving base. In coating and surface-sizing of paper or of an equivalent web material, two alternative methods and devices are used commonly, i.e. a blade coater or a bar coater. In particular in the surface-sizing technique, bar coaters have been used increasingly in recent years, because their usability has proved very good. In coating and surface-sizing, a bar coater is used for spreading and smoothing the coating agent onto the face of the paper or of an equivalent web material, the coating agent being usually applied to the web face by means of an applicator roll. In film size presses, the coating agent may also be applied directly onto the faces of the size-press rolls, from which rolls it adheres in the roll nip to the web running through the nip. As was already stated above, either a revolving coating bar or a coating blade can be used as the coating member. When the coating agent is applied, e.g., by means of a grooved coating bar onto the rolls in a size press, the roll end areas placed outside the web must be doctored clean by means of lateral doctors, because otherwise this coating agent remaining in the end areas of the rolls would cause considerable splashing in the roll nip. The doctoring of the lateral areas has proved very difficult, and it also abrades the roll face to a considerable extent. With the introduction of pigmenting with a high dry solids content, multiple problems have been encountered in the lateral areas on the rolls. The conventional lateral jets intended for surface sizing have usually been placed in a location in which they have been blocked readily, because the coating paste flows and splashes onto them. If the lateral jets are blocked, lubrication of the lateral areas is prevented, as a result of which the end areas of the rolls are easily damaged. It is a further, highly significant drawback of the conventional solutions that the lubrication water coming from the lateral jets passes directly into the recirculation of the coating agent, where it dilutes the coating paste. In pigmenting with coating pastes of a high dry solids content, the diluting waters must be minimized. Since the quantity of lubrication water must be minimized, the coating width cannot be controlled and limited sufficiently well, which has had the consequence that it has been necessary to employ lateral doctors, which again abrade the roll ends to a considerable extent, as was stated above. Nor do the lateral doctors operate reliably at high dry solids contents. Also, little quantities of water produce drying of the paste on the roll face, which again causes heating of the coating bar in bar coaters and heating of the coating blade in blade coaters, which may result in damage to the bar cradle and/or to the roll coating in the lateral areas. The object of the present invention is to provide a method and an equipment by whose means the above problems and drawbacks related to the prior art are avoided and solved. In view of achieving this, the method in accordance with the invention is mainly characterized in that, into the areas outside the coating width, substantially over the width defined by the lateral seals and the roll ends, liquid is sprayed onto the moving base, in its running direction, immediately before the coating member or directly into the nip between the moving base and the coating member to lubricate said nip and to dilute the coating agent that has entered into the areas outside the coating width, and that the excess amount of the sprayed liquid is collected off to prevent its entering into the recirculation of the coating agent, so as to prevent the coating agent from being diluted. Especially in the case of a grooved bar, it is also possible to employ water jets exclusively for lubrication and cooling of the end areas of the roll, in which case, before the bar, the lubrication water can be doctored, e.g., by means of a blade into a recirculation trough of its own. On the other hand, the equipment in accordance with the invention is mainly characterized in that, in the coating device, in the areas outside the coating width, substantially over the width defined by the lateral seals and the roll ends, in the running direction of the moving base, immediately before the coating member, jet pipes have been installed to spray liquid onto the moving base or directly into the nip between the moving base and the coating member to lubricate said nip and to dilute the coating agent that has entered into the areas outside the coating width, and that the coating device has additionally been provided with means for collecting off the sprayed excess quantity of liquid so that access of the excess quantity of liquid into the recirculation of the coating agent is prevented. By means of the solution of the present invention, compared with the prior art, a considerable advantage is obtained in particular in the respect that, in the invention, the lubrication water cannot be carried into the recirculation of the paste to dilute the paste, but the lubrication water is collected off separately. Especially in coating with coating pastes of high dry solids content, such prevention of dilution of the paste is a considerable improvement over the prior art. Since the lubrication water is collected off separately, the water can be used as larger quantities than in connection with the prior-art lateral jets, in which case the paste cannot be dried on the roll face even with high dry solids contents, so that any disturbance arising from such drying can also be avoided by means of the present invention. The further advantages and characteristic features of the invention come out from the following detailed description of the invention. In the following, the invention will be described in detail with reference to the figures in the accompanying drawing. Figure 1 is a fully schematic sectional view which illustrates a first embodiment of a coating device provided with an equipment in accordance with the invention. Figure 2A is an illustration taken in the direction of the arrow A in Fig. 1 of an equipment in accordance with the invention fitted in a coating device. Figure 2B is an axonometric view of the equipment as shown in Fig. 2A. Figure 3 is an illustration corresponding to Fig. 1 of a second embodiment of a coating device provided with an equipment in accordance with the invention. Figure 3A is an axonometric view of a detail of Fig. 3. Fig. 1 shows a device in accordance with the invention for coating or surface-sizing of a web material, by means of which device the pigment paste is applied to the face 1 of the roll by means of the "short-dwell technique" so that the size or pigment paste P is fed to the application zone, which is defined by the revolving bar 10, which operates as the coating member, by a dam blade 15 or an equivalent front wall of the application zone, by the roll face 1, and by lateral seals (not shown in Fig. 1). By means of the dam blade or front wall 15, the overflow of the size or coating paste from the application zone into the collecting trough (not shown) is regulated in the way known in prior art. The bar 10 that operates as the coating member is mounted revolvingly in the bar cradle 11, which is mounted conventionally in the bar-cradle holder 14, in which it is secured in its position by means of fastening or tightening means 14'. Behind the bar cradle 11, a loading hose 12 is provided, which acts upon the rear face of the bar cradle and which is mounted in a hose holder 13, which may also operate as a profile bar. By means of the loading hose 12, the coating member 10 is loaded with the desired force and pressure against the roll face 1. The dam blade 15 or the front wall is attached conventionally to a holder 16 of its own. In a coating device of the sort described above, an equipment in accordance with the invention is installed, comprising a jet pipe 17 placed in the transverse direction of the machine and a collecting trough 18, which are attached to the holder 14 of the bar cradle or to the fastening and tightening means 14' of the holder by means of fastening members 19, in the direction of rotation of the roll, as close to the coating bar 10 as possible before the nip between the coating bar 10 and the roll. The construction is illustrated in more detail in Figs. 2A and 2B. As comes out in particular from Figs. 2A and 2B, said construction that consists of the jet pipe 17 and the collecting trough 18 is fitted in the area between the lateral seal 20 of the application zone and the roll end, which is denoted with the dashed-dotted line and with the reference 1a in Figs. 2A and 2B. The jet pipe 17 is provided with a number of holes 17a that have been formed into the wall of the pipe, liquid jets being applied through said holes towards the nip between the coating bar 10 and the roll. The equipment that comprises the jet pipe 17 and the collecting trough 18 may be arranged to be displaceable in the transverse direction of the machine in view of permitting a ready adjustability of the coating width. In its simplest form, this adjustability is accomplished so that the fastening holes in said equipment 17,18, through which holes the equipment is attached to the bar-cradle holder 14 or to the fastening and tightening means of the holder by means of fastening members 19, such as screws, are formed oblong in the transverse direction of the machine. The spray equipment 17,18 may also be provided with transfer means (not shown), by whose means its location can adjusted even during operation of the machine. Further, it is possible that the spray equipment 17,18 is connected together with the lateral seals 20, in which case they are transferred together. In such a case, regulation of the coating width is even more efficient. The liquid to be sprayed is preferably water, into which air may have been fed so as to disintegrate the water into very small drops. By means of the liquid jets, the paste is diluted in the lateral areas of the roll, in which case the paste quantity in the lateral areas of the roll remains substantially lower, because the paste that flows into the end areas beyond the lateral seals has been diluted extensively by means of the abundant water, in which case, owing to the low hydrodynamic forces, the smooth bar, the smooth end area of a grooved bar, or the coating blade, which is used as the doctoring member, permits just a thin film to pass through the doctor. In some cases it is possible that the lateral doctors can be omitted completely. Thus, a little proportion of the liquid jets lubricates the nip between the bar 10 and the roll, whereas the rest of the sprayed liquid flows away, and this excess liquid is collected into the collecting trough 18, from which it is drained off so that the liquid does not enter into the coating-agent collecting trough to dilute the coating agent. As was stated above, the excess liquid is collected off, so that detrimental dilution of the coating agent cannot occur. In some cases, lateral doctors need not be used at all, because, owing to the liquid fed into the lateral areas, the liquid quantity coming through the nip between the coating bar 10 and the roll is so little that it does not splash at all in the nip in the size press. For example, if the lateral seals 20 are worn and coating agent, such as paste or equivalent, can flow into the lateral areas, the liquid quantity to be sprayed can be increased to such a high level that the dry solids content of the coating paste in the areas of the roll ends is lowered and the film layer between the coating bar 10 and the roll is sufficiently thin, so that lateral doctors are not needed. In such a case, the liquid quantity to be sprayed can be even several litres per minute for each end of the roll. Since the liquid quantities to be used are allowed to be large, the holes 17a in the jet pipe 17 may also be formed sufficiently large, in which case they cannot be blocked. Since the jet pipe 17 is placed immediately before the coating bar 10, in the direction of rotation of the roll, detrimental splashing of the coating agent, such as paste, cannot occur either, and in such a case the holes 17a in the jet pipe 17 remain open. Owing to the efficient lubrication and cooling, the coating bar 10 cannot be heated, in which case damage to the bar cradle and/or to the roll cannot occur either. In view of further improvement of the lubrication and in view of reduction in the friction between the coating bar 10 and the end area of the roll, it is advisable to add a lubricating agent suitable for the purpose to the liquid to be sprayed. Fig. 3 shows an alternative embodiment of the method and the equipment in accordance with the invention. Also in the embodiment of Fig. 3, the application of the size or coating-agent film onto the roll face 1 is carried out by means of the "short-dwell technique" so that, in the coating device, the size or an equivalent coating agent is fed to the application zone, which is defined by the revolving coating bar 30, which operates as the coating member, by the dam blade 35 or by a front wall of the application zone, respectively, by the roll face 1, and by lateral seals (not shown). By means of the dam blade 35 or the corresponding front wall, which is installed in a holder 36 of its own in the conventional way, the overflow of the size or coating agent from the application zone into the collecting trough (not shown) is regulated in a way known from prior art. The coating bar 30 is installed revolvingly in the coating-bar cradle 31, which is again attached to the cradle holder 34 in a known way. Behind the cradle 31 of the coating bar, a loading hose 32 is fitted, which acts upon the rear face of the cradle and by whose means the loading pressure of the coating bar 30 against the roll face 1 is regulated. In the coating device as shown in Fig. 3, in the coating-agent feed chamber 40, a feed pipe 42 for the coating agent, such as size or equivalent, is installed, which pipe is placed in the transverse direction of the machine and through which pipe the coating agent is fed to the application zone. The construction of the coating-agent feed chamber 40 and of the feed pipe 42 may be similar to that described, e.g., in the applicant's FI Patent Application No. 920618 of earlier date. In the construction in accordance with the invention, the construction and operation of the feed chamber and the feed pipe 42 are illustrated in more detail in Fig. 3A. Between the feed chamber 40 and the application zone, across the coating width, a plate 41 or equivalent is installed, into which a necessary number of through holes (not shown) have been formed, which holes are placed at a suitable invariable distance from one another in the transverse direction of the machine. From the feed pipe 42, the coating agent is fed through nozzles 44 that have been formed into the pipe, a large number of such nozzles being provided in the transverse direction of the machine at an invariable distance from one another across the coating width. Said nozzles 44 form a first throttle for the coating-agent flow. Also, a a second throttle is provided for the coating-agent flow, which second throttle comprises the through holes (not shown) that have been formed into the plate 41. By means of these throttles, the coating-agent flow can be passed as uniformly as possible to the application zone. As is the case in the embodiment of Fig. 1, so also in the solution shown in Fig. 3, a jet pipe 37 is fitted in the coating device, and the construction and operation of said pipe 37 may be similar to the construction illustrated in Figs. 1, 2A and 2B. Thus, through said jet pipe 37, liquid jets are fed, in the direction of rotation of the roll, as close as possible to the nip formed by the coating bar 30 and the roll face 1, before said nip. In the embodiment of Figs. 3 and 3A, the coating-agent feed chamber 40 has been divided by means of partition walls 45 into three separate compartments so that the middle compartment 40a covers the coating width, the partition walls 45 in the feed chamber 40 being placed substantially at the lateral seals (not shown). Thus, the nozzles 44 are also fitted in the feed pipe 42a exclusively in the area of the coating width, i.e. at the middle compartment 40a of the feed chamber. Thus, in the area of the middle compartment 40a, the coating agent is applied to the roll face 1 and the excess coating agent is made to flow to the recirculation (not shown). In the lateral compartments 40b of the coating-agent chamber, i.e. between the partition walls 45 and the roll ends, the feed pipe 42b is closed, so that in this area no nozzles have been arranged into the pipe. Thus, in the lateral compartments 40b, no feed of coating agent to the application zone takes place. Instead, in the areas of said lateral compartments 40b, spraying of liquid is carried out through the jet pipes 37 to the end areas of the roll so as to lubricate said roll ends. Likewise, in the areas of said lateral compartments 40b, the excess quantity of the sprayed liquid is collected off so that said excess liquid flows into said lateral compartments 40b in the feed chamber, from which it is drained off, e.g., through one or several openings 43 formed into the bottom of the feed chamber, so that the liquid does not enter into the recirculation of the coating agent to dilute the coating agent. Thus, the embodiment of Figs. 3 and 3A does not include the collecting trough shown in Figs. 1, 2A and 2B. Above, with reference to the figures in the drawing, the invention has been described in connection with a coating device in which the coating member is a revolving bar 10,30 resting against the roll face 1. Said bar 10,30 is preferably a smooth-faced bar, but the invention is also suitable for use in connection with a grooved bar, because, also in such a case, the same advantage is obtained in respect of prevention of dilution of the coating agent. Further, it is possible to employ the solution in accordance with the invention also in connection with a blade coater, i.e. in a coating device in which, in stead of the coating bars 10,30 shown in the figures in the drawing, a coating blade is used as the coating member. When coating is carried out by means of a blade, the problem of spreading of the coating paste is experienced even more clearly than when a coating bar i used, so that, by means of the solution of the present invention, said problem of spreading can also be brought under control in blade coaters. Further, the invention can also be applied to coating taking place directly onto the web. In such a case, in the embodiments shown in Figs. 1 and 3, the web would be passed along the roll face 1, and the coating agent would be applied by means of the coating members 10,30 directly onto the face of said web. Further, instead of limitation of the coating width, the invention can also be used exclusively in order to cool the coating member, to lubricate the nip between the coating member and the roll end area, and to keep the roll end areas clean. Thus, the invention is not restricted to the exemplifying embodiments illustrated in the figures in the drawing or to the embodiments described in the specification given above alone, but different embodiments of the invention may show variation within the scope of the inventive idea defined in the accompanying claims.

Claims: Method for limitation of the coating width and/or for prevention of damage to the roll ends in coating or surface-sizing of paper or of an equivalent web material, in which method the coating agent, such as size, coating paste or equivalent, is introduced into the coating device to an application zone defined by a coating member (10,30), by a moving base (1), by lateral seals (20), and by a front wall (15,35) and spread onto the moving base, such as a roll face (1) or a paper or board web that is passed over the roll, by means of the coating member (10,30) loaded against the moving base (1), characterized in that, into the areas outside the coating width (40a), substantially over the width (40b) defined by the lateral seals (20) and the roll ends (1a), liquid is sprayed onto the moving base (1), in its running direction, immediately before the coating member (10,30) or directly into the nip between the moving base (1) and the coating member (10,30) to lubricate said nip and to dilute the coating agent that has entered into the areas (40b) outside the coating width (40a), and that the excess amount of the sprayed liquid is collected off to prevent its entering into the recirculation of the coating agent, so as to prevent the coating agent from being diluted. Method as claimed in claim 1, characterized in that the liquid to be sprayed is introduced through jet pipes (17,37) transverse to the machine direction and fitted in the areas outside the lateral seals (20) of the coating device, the liquid being sprayed through a number of holes (17a) that have been formed into the walls of said pipes into the entire end areas defined by the lateral seals (20) and the roll ends (1a). Method as claimed in claim 1 or 2, characterized in that the excess amount of the sprayed liquid is collected off into collecting troughs (18) fitted underneath the jet pipes (17). Method as claimed in claim 1 or 2, characterized in that the excess amount of the sprayed liquid is passed away from the coating device through lateral compartments (40b) placed in the feed chamber (40) outside the coating width and defined by the lateral seals (20) and partition walls (45) or equivalent. Method as claimed in any of the preceding claims, characterized in that the liquid that is sprayed is water. Method as claimed in any of the preceding claims, characterized in that air is mixed into the liquid jets to disintegrate the liquid into small drops. Method as claimed in any of the preceding claims, characterized in that a lubricating agent is added to the liquid to be sprayed to lower the friction between the coating member (10,30) and the end area of the roll. Method as claimed in any of the preceding claims, characterized in that, in view of improving the regulation of the coating width, the equipment constituted by each jet pipe (17) and each collecting trough (18) is transferred in the transverse direction of the machine either separately or together with the related lateral seal (20). Method as claimed in any of the preceding claims, characterized in that, in stead of limitation of the coating width, in the method, by means of the spraying equipment (17,37), exclusively the coating member (10,30) is cooled, the nip between the coating member (10,30) and the end area of the roll is lubricated, and the end areas of the roll are kept clean. Equipment for limitation of the coating width and/or for prevention of damage to the roll ends in coating or surface-sizing of paper or of an equivalent web material in a coating device, which comprises an application zone defined by a coating member (10,30), by a moving base, such as a roll face (1) or a paper or board web that is passed over the roll, by lateral seals (20), and by a front wall (15,35), the coating member (10,30) that is loaded against the moving base (1) being fitted to spread and to smooth the coating agent, such as size, coating paste or equivalent, which has been introduced into the application zone, onto the moving base (1), characterized in that, in the coating device, in the areas outside the coating width (40a), substantially over the width (40b) defined by the lateral seals (20) and the roll ends (1a), in the running direction of the moving base (1), immediately before the coating member (10,30), jet pipes (17,37) have been installed to spray liquid onto the moving base (1) or directly into the nip between the moving base (1) and the coating member (10,30) to lubricate said nip and to dilute the coating agent that has entered into the areas (40b) outside the coating width (40a), and that the coating device has additionally been provided with means (18,43,45) for collecting off the sprayed excess quantity of liquid so that access of the excess quantity of liquid into the recirculation of the coating agent is prevented. Equipment as claimed in claim 10, characterized in that the jet pipes (17,37) are attached to the holder (14,34) of the coating member (10,30) or to the fastening and tightening means (40') of the holder, being placed as transverse to the machine direction, and their walls are provided with a number of through holes (17a), which are directed so that the liquid jets directly hit the nip between the moving base (1) and the coating member (10,30) or that the jets hit the moving base (1) immediately before the nip. Equipment as claimed in claim 10 or 11, characterized in that, underneath the jet pipes (17), collecting troughs (18) are provided so as to recover and to drain off the sprayed excess quantity of liquid. Equipment as claimed in claim 12, characterized in that the collecting troughs (18) are attached to the holder (14) of the coating member (10) or to the fastening and tightening means (14') of the holder. Equipment as claimed in claim 12 or 13, characterized in that the jet pipes (17) and the collecting troughs (18) are fixed by means of the same fastening members (19). Equipment as claimed in claim 10 or 11 in a coating device that is provided with a coating-agent feed chamber (40) transverse to the machine direction, through which feed chamber the coating agent is arranged to be introduced into the application zone, characterized in that the feed chamber (40) has been divided into three separate compartments in the transverse direction of the machine by means of partition walls (45), so that the feed of the coating agent into the application zone has been arranged through the middle compartment (40a) and the recovery and draining off of the sprayed excess quantity of liquid has been arranged through the lateral compartments (40b). Equipment as claimed in any of the claims 10 to 14, characterized in that the spraying devices consisting of the jet pipes (17) and of the collecting troughs (18) are arranged displaceable in the transverse direction of the machine. Equipment as claimed in claim 16, characterized in that said spraying devices (17,18) are connected together with the related lateral seals (20) so that said spraying devices (17,18) and lateral seals (20) can be shifted together.

Inventors: KORHONEN HANNU, LUMMILA MARKKU, RANTANEN RAUNO, KORHONEN, HANNU, LUMMILA, MARKKU, RANTANEN, RAUNO
Applicants: VALMET CORP, VALMET CORPORATION
Application year: 1994
Main classification: D21H23
IPC codes: D21H23